Today's automobiles generally employ pneumatic wheels, in which a bead of a tire is sealed with a rim of the wheel to provide an inner space filled with air to a predetermined pressure such that the tire is expanded to form an annular shape appropriate for driving.
The tire of a pneumatic wheel maintains the shape of the wheel and provides a drive function and ride comfort using filled air pressure. Therefore, if the tire is pierced or damaged by a sharp object such as a nail or glass shard, or loses too much air pressure due to some other cause during operation of the vehicle, the annular shape of the wheel is likely to be deformed and lose its function. In more serious cases, a tire cord and rubber may be separated or cut causing the tire to be torn apart so that the vehicle becomes impossible to drive. When the vehicle is driven with a flat or torn tire, the expensive wheel, suspension, and so on, of the vehicle may be damaged. And at high speeds, serious accidents may occur.
U.S. Pat. Nos. 4,067,374 and 4,193,437 disclose a run-flat tire including reinforcing rings inserted into its sidewalls to support the weight of the vehicle and allow it to be driven a certain distance when flat, for the sake of drivers who are unable to change a flat tire, for example, the handicapped or women when a tire of a pneumatic wheel is flatted due to blowout. In addition to the reinforcing rings, the sidewalls of the run-flat tire have a large amount of rubber in order to prevent buckling when there is no air in the inner space. However, compression, shearing stress and heat imparted to the tire due to repeated loads during driving cause fatigue fractures in the sidewalls. In addition, the thick sidewalls, which aim at safety, reduce ride comfort.
A more advanced concept than the run flat tire is a non-pneumatic wheel, various types of which have been proposed to avoid tire blowout.
For example, U.S. Pat. No. 5,050,656 and Korean Patent Application No. 2004-7002607 disclose a “Non-Pneumatic Tire Wheel” and a “Non-Pneumatic Tire”, respectively, which have been developed for the purpose of preventing blowout of the tire. However, since the tire employs plate-shaped spokes to absorb shock through yielding and reflecting movement, excessive noise and heat generated when driving the vehicle and relatively poor ride comfort in comparison with the pneumatic tire are obstacles to commercialization of the non-pneumatic tire.
In addition, Japanese Patent Laid-open Publication No. 2008-074345 discloses a non-pneumatic wheel including a plurality of link mechanisms between a tread of a tire and a rim of the wheel, and spring members interposed between the link mechanisms. However, since the link mechanisms and the spring members are formed as one integrated body, the tread can absorb only shock perpendicular to the road surface and does not properly absorb local shock.
Further, Japanese Patent Laid-open Publication No. H9-058209 discloses a wheel including a plurality of leaf springs mounted thereon, and rubber mounted on tips of the leaf springs. However, it is impossible for the wheel to stably maintain an annular shape like the pneumatic wheel, and a part that contacts the road cannot be optimally subdivided. Thus, noise due to shock is loud and ride comfort is reduced.
Meanwhile, an ultra high performance (UHP) tire having tread formed of a compound material manufactured by mixing various chemicals and rubber, rolling the mixture, and refining the mixture to increase road holding is coming into use. However, it is impossible to subdivide the tread according to function within the structure of the pneumatic wheel in which the tread is uniformly biased outward by air pressure.
Moreover, conventional wheels transmit friction and vibration noise from the tires through the vehicle body to the inside of the vehicle, thereby increasing noise inside the vehicle.